A voice broke through the crackle on the police radio, saying, "Suspect has failed to yield."

Officer Steve York patted his chest to activate a camera mounted on his sunglasses, then pounded the gas pedal. A high-speed chase through the streets of Mesa, Ariz., followed with cameras -- his and ours -- rolling.

There have been reality shows about cops in the past but, for the first time, cameras about the size of a cigarette lighter are revealing a cop's true reality and providing them with evidence to help protect officers from false accusations.

Every morning, York, a former Marine and 19-year veteran of the Mesa Police Department, grabs his handcuffs, gun and Axon Flex camera. The bullet-shaped, 3.2-inch camera, made by Taser, can record as much as 12 hours of footage and is fast becoming a lifeline in York's daily patrols.

He has been testing his camera for months as law enforcement agencies debate whether or not to roll out more widely cameras that some say will reinvent police work in the United States.

"For me, this camera is not a big deal. A lot of officers don't want to wear it," York said. "Some guys are like, 'It's big brother,' but our videos don't get reviewed. Our videos only get reviewed if we go to court or if someone complains they were mistreated. If you were recording, you can then say, 'Here is the video.'"

Here's how it works: The Axon camera is strapped to an officer's chest, along with a record button. When an officer hits record, the video starts 30 seconds prior to when he hit the button. It captures every scream, alley-way race and confrontation with clear audio.

At the end of his shift, York takes the camera off his glasses and slides it into the Evidence Transfer Manager program, which downloads the footage and then uploads it to Evidence.com, a website maintained by Taser.

York has used the camera to film everything from mundane traffic stops and shoplifting judges to drugged-out, dangerous individuals, on whom he said he had to use a stun gun in order to subdue.

While "Nightline" was on his beat, his cameras and ours captured a custody dispute, suspected gun incidents, breaking-and-entering in a daycare center and a high-speed chase involving several officers trying to stop an individual who "failed to yield."

"I don't see any problem with this camera, whatsoever," York said. "It makes your reports that much more accurate."

York is one of 50 officers in the department that have been issued the "capture everything" Axon cameras. Mesa Police Chief Frank Milstead said the cameras are the future.

"The idea is if people are going to videotape my officers from their vantage point and only put up the provocative part of the video on some posting, I want to be able to have the entire conversation with all the other things, the radio traffic, the ambient noises. I want to have an accurate picture," Milstead said.

Milstead added that the cameras, which cost about one-third of the average dash cam, may save his department and others thousands of dollars for fighting against false accusations leveled at his force.

"People are much politer when they know they are being videotaped and that it may be used later," he said. "All I have to do is save myself a couple of lawsuits with a tape and it pays for itself."

Cops in more than 600 departments and growing are now being fitted with Axon cameras, which has already captured millions of police interactions across the country that have been uploaded to Evidence.com. Once the officer records the incident and ingests the material, Taser said it creates a digital fingerprint aimed at preventing alterations.

"We want police to be ready for the tidal wave of information in the digital age. Every cell phone has a camera and there are four people standing around with a cam, and now officers are saying maybe I should have my own," said Taser CEO Rick Smith. "The breakthrough is: What do you do with all this data? ... From the moment the file is on the device, we take a digital fingerprint and we can match that file to see if anything has changed. It is stronger than DNA technology that is accepted in the courts."

Studies are beginning to trickle in about the impact of the Axon. A study by the Rialto California Police Department found that, after a year of its force using them, overall complaints of police brutality plummeted 88 percent, and use of force dropped 60 percent.

"This is the answer to the Rodney King video, 20 years later," said Scott Greenwood, chief counsel of the ACLU. "It's the next big thing. ... The officers who don't want to use one should be the first one to get them. In the vast majority of cases, officers are doing what we expect them to do. For those few times when officers commit misconduct or do something unconstitutional or illegal, we will have that evidence."

The unusual partnership between law enforcement and the ACLU is not surprising, said Greenwood, who believes that in 10 years the cameras will be as ubiquitous as handcuffs.

"Technology is neutral and, with good policy, you are going to see accountability go up," he said. "It will make policing much more transparent. It will make officers behave better and it will put people on their best behavior."

Greenwood and the ACLU are pushing law enforcement agencies to adopt a set of recording protocols that each officer must follow when using the devices. He said he sees a potential danger in giving officers the ability to use the cameras however they choose. Right now, most officers can choose what to record and when.

For now, York said, he plans on recording every call he is involved with. At the end of his shift, he went home knowing that every police interaction he was involved in that day can be viewed and reviewed. And he is perfectly fine with that.